The use of torque limiting clutches between input power sources and output mechanisms is well known. Typically, a torque limiting clutch has a characteristic breakaway torque allowing slippage between input and output shafts or mechanisms when the torque on the shafts exceeds the characteristic breakaway torque of the clutch.
Some machinery that employ torque limiting clutches use hollow shaft motors. For example, various pieces of underground mining equipment use hollow shaft electric motors to drive work implements. These motors commonly have a torque limiting clutch attached to one end, with the clutch input secured to the hollow motor shaft. The output of the torque limiting clutch is connected to an output shaft, or torque shaft that delivers torque to a work implement or a gear reduction box. Typically, the output shaft travels back through the motor inside the hollow motor shaft. The purpose for such an arrangement is to provide for easy accessibility to the clutch for servicing and to position the clutch on the opposite side of the motor than the work implement. When in use, the work implement may encounter a jam that acts to suddenly declerate the motor, creating a high level of torque. The purpose of the torque limiting clutch is to prevent this high level of torque from damaging the drive system components.
Access to a torque limiting clutch is necessary because the clutch must be disassembled to replace worn friction elements in the clutch and other maintenance activities. Access is also required because the clutch must be disassembled so that the input can be secured to the motor shaft. It is thus desirable to have a torque limiting clutch that is easy to disassemble and reassemble and is generally positioned in an accessible location.
A torque limiting clutch of a desirable nature, capable of achieving the benefits presented above, is presented and described in U.S. Pat. No. 5,688,176 for Multiple Disc Torque Limiter for Hollow Shaft Motors, owned by the assignee of the instant application. While this prior art device achieves some level of compactness, the implementation and utilization of spring cup assemblies are a limiting factor in size reduction and, it is desirable, to eliminate reliance on such spring cup assemblies in applications of the nature under consideration.
It is desirable that the overall structure and configuration of a compact torque limiter be such that the overall size, and particularly the axial length, be minimized It is further desirable that the friction area or region of a compact torque limiter of the nature under consideration be capable of being shielded or sealed from external contaminants present in the operational area. Yet further, for enhanced operability and adaptability, the utilization and implementation of speed sensors, wear indicators, and the like are deemed desirable, provided that they do not add to the overall size of the operational unit.
It is further most desirable that a torque limiting clutch of the type under consideration be given to ease of serviceability and refurbishment. To that end, it is desirable that the friction element of the clutch assembly be maintained as an integral unit and a portion of the output hub assembly which may be easily removed from the clutch assembly itself such that friction and separator elements may be removed, refurbished and replaced, along with any other parts requiring such servicing.